The background description provided here is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Substrate processing systems may be used to perform ashing, deposition and/or etching of film on a substrate. Substrate processing systems typically include a processing chamber with a substrate support such as a pedestal, an electrostatic chuck, a plate, etc. A substrate such as a semiconductor wafer may be arranged on the substrate support. In chemical vapor deposition (CVD) processes, a gas mixture including one or more precursors may be introduced into the processing chamber to deposit a film on the substrate. In some substrate processing systems, plasma may be used to activate chemical reactions.
To obtain high quality film, it is important to deliver the precursor gas to the processing chamber with a desired concentration. The precursor may be a solid that is sublimated or liquid that is evaporated into carrier gas to provide the precursor gas. In some substrate processing systems, precursor flow may be measured using a mass flow sensor. However, mass flow sensors typically have issues with high temperature, low pressure, and/or low pressure drops that may be used. Other ways of measuring gas concentration include infrared sensors (IR), Fourier Transform Infrared (FTIR) spectrometers, and ion mass spectrometers. However, these approaches typically have high cost or do not generate a signal characterizing the concentration of the precursor gas.